Fluid motor



C. B. LIVERS June 14, 1966 FLUID MOTOR Filed Jan. 22, 1963 QQLOS B.Ln/Ezs NVENTOR ATTOQN EVS United States Patent O 3,255,638 FLUID MOTORCarlos B. Livers, North Hollywood, Calif., assignor to SpragueEngineering Corporation, Gardena, Calif., a corporation of CaliforniaFiled Jan. 22, 1963, Ser. No. 253,130 2 Claims. (Cl. 74-60) Thisinvention relates to uid motors of the wobble plate type such as shownin United States Letters Patent 2,994,306 and the present invention hasto do with improvements upon such motors.

In some servo mechanism applications it is common to have substantiallyequal pressures simultaneously applied to both the inlet-and outletports of the motor. Under such conditions most piston-type fluid motorstend to lock and, even under conditions of no load, require a verysubstantial differential pressure between the inlet and outlet ports inorder to cause the motor to operate. Even then the motor is apt to runrough and this renders it unacceptable for use with delicate mechanisms,The cause of this locking is the fact that all the pistons are underpressure and the heavy loads that result are additive to the side loads,bearing loads and general friction.

An object of the invention is to provide a novel construction in a uidmotor of the piston-and-wobble plate type which overcomes the abovenoted disadvantage of other fluid motors of this type and which enablesthe motor to operate easily and elfectively on only slight differentialof pressure between the inlet and outlet ports, irrespective of the factthat both ports may be subjected to'high pressure. v

To accomplish this it is an object of the invention to provide means formaintaining pressure in the motor casing which is approximately equal tothe lowest pressure applied to the two ports of the motor. When this isaccomplished all the forces which are ordinarily applied to one-half thepistons during their return strokes are canceled, and the forces whichare ordinarily applied to the other half of the pistons during theirpower strokes are reduced to that amount represented by the differentialpressure. Thus this greatly reduces the total forces customarilyencountered and permits the motor to operate smoothly and with lowdifferential pressure and good sensitivity.

More specifically it is an object to provide novel means forpressurizing the interior of the casing beyond the cylinders and thepistons by utilizing the pistons as a means of carrying fluid pressurethereto. It is therefore an object to provide a novel pistonconstruction which permits bleeding pressure uid through the pistons.

Another object is to provide a novel piston and slipper constructionembodying fluid passage means for pressurizing the interior of thecasing.

Still another object is to provide a novel shaft seal arrangement whichpermits return of leakage uid to the system.

A further object is to provide a novel wobble plate assembly and a novelpiston and slipper assembly in combination therewith.

These and other objects will be apparent from the drawing and thefollowing description. Referring to the drawing:

FIG. l is a central longitudinal section through a motor embodying theinvention; v

FIGS. 2, 3 and 4 are cross-sectional views on lines 2 2, 3 3 and 4 4,respectively, of FIG. l;

FIG. 5 is an enlarged sectional view of a slipper and the adjacent endof one of the pistons; and

FIG. 6 is an elevational view of the end face of the slipper on line 6 6of FIG. 5.

More particularly describing the invention, the motor including a shellor casing 11 having radial ports 12 and 3,255,638 Patented June 14, 1966ice together with the cylinder block provide uid passages to thecylinders from an annular space 23. Each cylinder also has a port 24leading to the annular space 25 communicating with port 13. In eachcylinder 17 is -a piston 26 having a radially reduced center portion 27.Each piston acts as a valve to control flow of iluid to one of the othercylinders in the manner described in U.S. Patent 2,994,306. Also, thecylinder block 16, inner body 20 and shell 17 are joined as by brazinginto an integral unit.

The pistons 26 operate against a thrust plate 30 of a wobble plateassembly 31. The latter is mounted on a tubular shaft 33 joumaled inbearings 34 and 35 in the body 20 and mounting plate 15, respectively.An inner,

having an angularly disposed outer cylindrical surface 41,

the bushing being ixed to shaft 33 by pin 42. Mounted on the bushing aretwo thrust plates, designated 30 and 44, a spacer 45 and a bearing 46.The thrust plate 30 provides a surface 30 against which the pistons canoperate and, by virtue of bearing 46 between the two thrust plates,plate 30 can rotate independently as required. Behind plate 44 is awobble plate 50 having an inclined forward surface 51 and a rear surface52 which is normal to the axis of the shaft 33 upon which the wobbleplate is mounted and secured by pins 53. Axial thrust is taken by abearing 54 which is supported on a radially reduced section 55 providedon the inner end of the mounting plate 15. A bearing thrust plate 57 islocated behind the bearing.

Each piston is fitted with a slipper 60 and this comprises a body 61having a working face 62 adapted to abut the Athrust surface 30' ofthrust plate 30. Each slipper has a spherical-Shaped recess 63 receivingthe lball head 64 at the end of an associated piston, the lip portion 65Ibeing swaged over the head to retain it. The several slippers areretained in relatively close contact with the thrust surface 30 duringconditions when there is no hydraulic pressure available to do this by aspider comprising a plate 66 having apertures 67 receiving the slippersanda ball section 68 adapted to bear against a concave spherical bearingsurface 69 of a bearing 70.

`In order to pressurize the space or chamber 72 beyond the cylinders,each piston is provided with a uid passage 73 therethrough and in likemanner each slipper has a fluid passage 74 therethrough whichcommunicates with the passage in the piston. The y'working face 62 ofeach slipperl is provided with an inner groove 76 which is connected tothe passage -74 .by a radial groove 77. -An ou-tergroove 78 is connectedto the space around the slipper by a radial groove 79.

y It will be apparent that, in the operation of the motor, pressurefluid will pass through the pistons and slippers into chamber 72 whichis sealed and pressure will then build up in this chamber. Fluid underpressure may move through the pistons and slippers and occupy areasunder the slippers which are determined .by the areas of the grooves inthe working faces 62 thereof. The areas of such grooves are smaller thanthe diameter of the piston in orderthat the forces tending to separatethe iFurther it will be apparent that since the casing isV closed orsealed the pressure inside the casing willl rise until it reaches apressure slightly greater than the return pressure. Consequently a smallforce exists which tends to lift the slippers olf the face 30 of thethrust plate 30. The amountby which the force can lift the slippers iscontrolled by the longitudinal clearance in the bearings of the motor.This clearance should be suicient to permit adequate drainage of thecase liuid back through the returning pistons and into the returnsystem. There results a casing pressure slightly higher than the returnpressure.

In view of the high pressure in the casing a two-stage shaft seal isused. The first stage consists of a sleeve 80 which lits the shaftclosely and which carries a resilient seal ring 81 in a peripheralgroove 82. Beyond this is a second seal 83 which may be a flexiblemember of any suitable conventional construction. Such fluid as leakspast the first seal 80 is returned to the system through a passage 85and return port 86.

Although I have shown and described preferred forms of my invention, Icontemplate that various changes and modifications can be made thereinWithout departing from the invention, the scope of which is indicated bythe following claims. Also, it should be understood that while theinvention is primarily designed for yuse as a fluid motor, it is alsooperable as a pump when the shaft is turned by an external prime mover,and, consequently the word motor in the claims should be interpreted asinclusive of a pump.

I claim:

I1. In awobble plate type motor, a casing, a cylinder block in saidcasing having a plurality of cylinders disposed equidistantly around andparallel to a common axis, a shaft journalled in said casing on saidaxis, a wobble plate fixed to said shaft and having an inner surfacedisposed angularly transverse to the shaft, a bushing fixed to the shaftinwardly of and adjacent to the thrust plate and having a cylindricalouter surface whose axis is normal to the plane of the inner surface ofthe wobble plate, `a thrust plate assembly including a pair of annularthrust plates and bearing means therebetween, said assembly beingmounted on said bushing against the inner face of said wobble plate, andpiston means in each cylinder .bearing against said thrust plateassembly.

2. The wobble plate type lm-otor set yforth in claim -1 in which saidshaft comprises a hollow outer mem-ber journalled in said casing and aninner member extending from the region of said wobble plate to andbeyond the outer end of said outer member, said inner member being ofless diameter than the inner diameter of the outer memlber lwhere ittraverses .the same except at its inner end, and means tixedly securingthe inner end of said inner member to said outer member.

References Cited by the Examiner UNITED STATES PATENTS 1,958,221 5/19'34Wilcox 277-59 2,273,129 2/ 1942 Messinger 277-59 2,498,679 2/1950 Hall74-60 2,733,619 2/1956 Smith 74--569 2,776,628 l/ 1957 Keel 74--60 X2,944,430 7/1960 Huber 74-60 2,979,037 4/1961 Budzich 1211-119 2,997,9567/ 1961 Stewart 74-60 X 3,049,940 8/ 1962 yNeff et al. 74--569 3,056,38710/ 1962 Budzich 12-1-119 BROUGHTON G. DURHAM, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner.

W. L. FREEH, F. E. BAKER, Assistant Examiners.

1. IN A WOBBLE PLATE TYPE MOTOR, A CASING, A CYLINDER BLOCK IN SAIDCASING HAVING A PLURALITY OF CYLINDERS DISPOSED EQUIDISTANTLY AROUND ANDPARALLEL TO A COMMON AXIS, A SHAFT JOURNALLED IN SAID CASING ON SAIDAXIS, A WOBBLE PLATE FIXED TO SAID SHAFT AND HAVING AN INNER SURFACEDISPOSED ANGULARLY TRANSVERSE TO THE SHAFT, A BUSHING FIXED TO THE SHAFTINWARDLY OF AND ADJACENT TO THE THRUST PLATE AND HAVING A CYLINDRICALOUTER SURFACE WHOSE AXIS IS NORMAL TO THE PLANE OF THE INNER SURFACE OFTHE WOBBLE PLATE, A THRUST PLATE ASSEMBLY INCLUDING A PAIR OF ANNULARTHRUST PLATES AND BEARING MEANS THEREBETWEEN, SAID ASSEMBLY BEINGMOUNTED ON SAID BUSHING AGAINST THE INNER FACE OF SAID WOBBLE PLATE,SAID PISTON MEANS IN EACH CYLINDER BEARING AGAINST SAID THRUST PLATEASSEMBLY.